We are interested in the recognition and transport of antibodies by Fc receptors. Using a combination of X-ray crystallography, biochemistry, electron tomography, and confocal fluorescent microscopy, we have been investigating the neonatal Fc receptor (FcRn) and its interactions with IgG, focusing on defining the pathway by which FcRn-IgG and/or FcRn-Fc complexes are transported in intracellular endosomes across epithelial cell barriers. We now seek to build upon our initial electron tomography results, which defined the pathway of FcRn-mediated transcytosis across intestinal epithelial cells, by combining electron tomography, which allows 3D imaging of cells, with live cell fluorescent imaging, which can be used for 4D studies (3D plus time). Many of the Fc receptors for which we have high-resolution X-ray structures also transport antibodies through endosomes, therefore we plan to extend our imaging studies to other Fc receptor systems.